Presenter's biography

Biographies are supplied directly by presenters at OFFSHORE 2015 and are published here unedited

Stephanie Mann is in her second year of her EngD with the Industrial Doctorate Centre in Offshore Renewable Energy. Having completed a taught year in Offshore Renewable Energies at Edinburgh University, she is now based at the E.ON technology centre in Ratcliffe, Nottingham. Stephanie has been researching high altitude wind resource, and focusing on energy yield for airborne wind turbines.

Abstract

Wind yield assessment for airborne wind energy

Introduction

Airborne Wind Energy (AWE) is a novel form of harnessing wind energy. The potential benefits include higher energy output due to the increased wind velocities and more persistent nature of the wind at higher altitudes (100m-1000m). Also, the overall cost of the system is reduced since large, steel devices are not required. This results in a potential step down in the cost of energy for offshore wind systems.

Approach

One problem the AWE sector faces is its understanding and evaluation of the available resource at such high altitudes. There is evidence of low level coastal jetting and reverse shear at heights as low as 100m. Since met masts normally operate at heights up to 80m, non-typical wind data sets are required for an accurate assessment of the wind speeds. Virtual Met mast data has been aquired and assessed for the purposes of this assessment.

Main body of abstract

Offshore, conventional wind turbines are increasing in size and can have hub heights of up to 100m above sea level, and tip heights of over 150m. Standard shear profiles and models are only valid to a height of around 100m, but above this level the atmosphere is in a transitional zone between the upper and lower surface boundary layers. The wind speed isn’t only affected by frictional shear but also by the bulk properties of the atmosphere. This can result in errors in both the energy yield assessment and loading calculations for the offshore wind sector.

Twenty years of virtual met mast data has been acquired for several offshore sites. This data has then be used to calculate a yield estimate for two types of airborne wind energy converters. It has been assumed the airborne devices can vary height with time in order to access the highest available resource.

The airborne devices have been shown to have capacity factors of around 69%, which is almost double the capacity factor of a conventional turbine with a comparable power rating. The controllability of the turbine plays an important part in the performance of the turbine. Also, the available power to an airborne device varies with cos^{3}(a), where a is the angle the tether makes with the ground. Therefore, a longer tether can increase the power output for a generic airborne device, but this can increase the drag experienced.

Conclusion

These preliminary results show that AWE converters can a provide reliable, inexpensive form of wind energy. The knowledge gained about high altitude atmospheres is also vital to ensure the conventional wind industry can have accurate and reliable yield estimates as turbine sizes increase. Further work will be carried out to evaluate the wind data, and to investigate how the stability of the atmosphere affects the shear profile at the upper surface layer.

Learning objectives
This paper aims to give the reader information about how to perform an accurate yield assessment at high altitudes for large offshore and airborne wind. The benefits of airborne wind are also outlined.

Co-organiser:

Supporters:

EWEA is the voice of the wind industry, actively promoting wind power in Europe and worldwide. It has over 600 members, which are active in over 50 countries, making EWEA the world's largest and most powerful wind energy network.